Corrosion resistant alloy



United States Patent ice Patented Dec. 15,- 1964 Therefore such alloyswhile being extremely useful at 3,161,503 normal or. so-called roomtemperature are restricted in COOSION RESISTANT ALLO Gilbert A. Lenning,Las Vegas, and Barry W. Rosenberg,

Henderson, New, assignors to Titanium Metals Corpodesirableembrittlement during such a long exposure time.

practical applications, and do not appear to be suitably employedexposed to relatively high temperatu'res'for ration of America, New Yak,NY. a corpmafion of 5 even a short period of time, or even moderatelyelevated Delaware 7 temperatures durlng along period. N0 Drawing FiledSept 27, 19 1, g 141,003 It IS therefore a principal ob ect of thisinvention to 2 Claims. (Ci. 75-174) provide an improved corrosionresistant alloy. Another object of this invention is to provide athermally stable This invention relates to corrosion resistant alloysand 10 corrosion resistant alloy. Another object of this inven moreparticularly to alloys containing titanium and tantion is to provide animproved thermally stable and co rtalum having corrosion propertiesapproaching those of rosion resistant alloy having corrosion resistantproperties pure tantalum, and alos being thermally stable. approachingthose of pure tantalum but which can be The excellent corrosionresistant properties of alloys produced at substantially lower cost.Another'object of containing titanium and relatively large percentage oftanthis invention is to provide a corrosion resistant alloy postalum areknown. Such alloys are described in U.S. Patsessing high strengthtogether with good ductility, and ent 2,964,399. In addition to binaryalloys of titanium which is corrosion resistant and thermally stable.These and tantalum, alloys in which the tantalum is in part reand otherobjects of this invention will be apparent from placed by columbium arealso described in this patent. I the following description thereof. 4Such alloys are substantially less costly than pure tanta- Thisinvention in its broad aspects contemplates corrolum but approach thecorrosion resistance of tantalum in sion resistant alloys characterizedby thermal stability, their ability to Withstand corrosive effects ofsolutions and consisting essentially of from 40 to 70% by weight such asboiling hydrochloric, sulfuric, phosphoric or oxtantalum, and a betastabilizer selected from the. group alic acids. While these alloys dopossess remarkable and consisting of vanadium, molybdenum, chromium,iron valuable .corrosion resistant properties, it has been found andmanganese and mixtures thereof in amount from 2% that they are notthermally stable. When exposed to ternto 20% by weight, balancetitanium. The thermal stabilperatures of the order of several hundreddegrees Fahrity of the alloys of this invention is indicated bysubenheit they tend to become brittle. This embrittlement stantialretention of ductility rafterexposure to tempera: can lead tocatastrophic disintegration, and complete loss tures up to about 800 F.Optionally the alloys of this of their structural integrity. It isinteresting to note in invention may include up to 2.5% by Weight ofgl pthis connection that the reactions responsible for this em- 1mm, andadditional advantages will be derived from its brittlernent appear to befunctions of both temperature inclusion. A preferred range of betastabilizing content and time, and while they are clearly evident afterexis from 5% to 10% by weight within Which'theoptimum posure of such analloy to a temperature of several hunadvantages provided by the betastabilizer inclusion are dred degrees Fahrenheit in a relatively shortspace of obtained. Up to 15% by weight'ofcolurnbium may be time, thesame embrittling effect occurs at lower temperemployed in the alloy 'ofthis invention to replace a atures after an extended period of time.Since, by their similar percentage of tantalum, the tantalum andcolumnature, corrosion resistant alloys are expected to provide biumbeing present in the aggregate within the range from often many years ofservice, even a slightly elevated tem- 40% to 70% by Weight and withtantalum content 35% perature during their normal useful life canproduce un- 40 to 70% by weight. A particularly effective and desirablealloy composition consists essentially of about by Table 1 V CORROSIONTESTS OF VARIOUS ANNEALED TITANIUM-TANTAL UM ALLOYS IN VARIOUS BOILINGMEDIA artists Corrosion Rate, MilsPer Year Heat; Exposure i No.Composition Time,

Hours 20% 30% 3% Oxalic H01 H1504 H3PO4 ,Acid

48 0.1 48 0.6 48 0.3 48 0.7 Ti-40Ta-100b-2 168 4.8 '1i-40Ia10(lb-5V. 1684.7 Ti40'la-10Cb-7V 48 8:1 Ti-40Ia-100b-1OV 24 0. Tl-40Ta-10Cb-10V 51 r0.89 Ti-40Ta-10Cb-10V... 168 0. 45 Ti-40Ta-100b-10V... 336 0.34Ti-40Ta-10Cb-10V.-. 672 0. 20 'Ii-40Ta-10Cbd2V... 48 -9.5Tl-40Ta-10Cb-16V 48 4.9' Ti-40 Ta-10Cb-20V 48 6. 2 Ti-40Ta-10Cb-3Cr 242. 62 Ti 40'1a-100b 301;. 51 1. 21 TTa-10Ob 3Cr 168 0.75T140Ta-10Cb-3Or. 336 0.41- Ti-40'Ia-10Cb-3Cr 672 0.25

weight of tantalum, about 1.5% by weight aluminum, about 8.5% by weightvanadium, and the balance titanium. Another very desirable specificalloy composition in which a portion of the tantalum content is replacedby columbium, consists essentially of about 40% by weight tantalum,about% by weight columbium, about 1.5% by weight aluminum, about 8.5 byweight vanadium, and the balance titanium.

Table l, preceding, shows the results of corrosion tests on a number ofalloys whose composition is shown as percentages by weight of alloyingingredients, balance titanium. The ingredients for each alloy weremelted in an arc furnace into a small ingotwhich was remelted severaltimes to insure homogeneity. The remelted ingot was rolled to form sheetof thickness about 0.040 inch, andthe rolled sheet was annealed at1400l500 F. for a period of /2 to 1 hour. Sections of sheet were cut toform coupons which were immersed in boiling acids of composition shown.Corrosion rates were calculated from weight loss.

Another group of alloys were similarly fabricated and tested forcorrosion resisting properties by immersion in boiling HCl for 48 hours.The results of these tests are shown below in Table 2.

Table 2 FOR'IY-EIGHT HOUR CORROSION TESTS OF VARIOUS TITANI UM-TANTALUMALLOYS IN BOILING 20% HO] 4 Table 2Continued FORTY-EIGHI HOUR CORROSIONTESTS OF VARIOUS TITANIUM-TANTALUM ALLOYS IN BOILING 20% H01 CorrosionHeat No. Composition Rate,

Mils/Year Ti-50Ta-20V. 3. 6 1.7 3. 5 1.2 4. 2 41. 0 24. 0 9.8 32. 0 7. 9T140'la-1OCb-10V-1.8Al I 17. 0 Ti-40Ta-l0Ob-12V-2JAL, 5. 8Ti-40Ta-100b-1Fe 2. 6 'li-40'Ia-l0Cb-2 Fe. 14. 0 Ti-40Ta-l0Cb-4Mn. 5. 9Ti-60Ta-8.5V-l.5Ai 0. 9 Ti-05Ta-8.5V-l.5Al 0. 4 Ti-GOTa-fiV-lAl 0. 9Ti-50la-10Cb-6V-1A1 1. 2

I N.D.No determination. I Surface iiaw in specimen.

It will be seen from Tables 1 and 2 above that alloys of this inventionshow excellent corrosion resistant properties. Materials resistingcorrosion to the extent that their corrosion rates are less than 50 milsper year in any given medium are rated as Class B, while those show-Corrosion ing less than 5 mils per year are rated as Class A. It is Heatf f evident by comparison with alloys of 50% titanium, and 50% tantalum,or 50% titanium, tantalum, and 3 6 10% columbium, that the corrosionresistance of these 014 alloys has not been materially affected by theaddition of beta stabilizers according to this invention, and within the0. 2 limits herembefore defined.

To determine thermal stability, the same types of alloysTi-52Ta-3.5Cr-l.5Fe 7.2 tested for corrosion were fabricated to sheet inthe same @kggggggiigg: 2:2 manner as those whose properties are shown inTables 1 Ti'-58Ta-3.5Cr-l'.5Fe 3.5 40 and 2 (many of these being thesame heats) and angijggggjgggffl fif ii nealed, exposed to elevatedtemperature and tested for '11-52'1a-s.5v-1.5A1.-- 1.3 strength andductility. The sheets were annealed at gjgggjgzgxjgfi: 1400 F. or insome cases 1500 F. for /2 to 1 hour, air- Ti-58Ta-8.5V-1.5Al.- 2. 0cooled, then heated for from 6 to 24 hours at mostly from $i328$1535i 3j 3:; 500 F. to 800 F. Specimens were prepared and tensile g-soga-iogb-scgr n 10.5 strength (ultimate and yield) and elongationdetermined ,;3 g }3 e 2:2 on some, while on others bend tests were runto indicate i-g8%a-188lg---g ductility. Bend tests show the minimum bendradius, ex- I I '5, j: pressed as times the sheet thickness, which couldbe made l'gg% 'g6- i;- in a specimen Without cracking; such a testcorrelates iI I Io13o 1 Well with ductility indicated by elongationduring tensile Ti-55Ta-8.5V-1.5Ai-0.2O1. 1.5 i e a T1 55Ta 8.5V 1 5M0302 L9 test rig In each cas a specimen of the alloy s an Ti 4OTa wOb 5Gr8 nealed was tested to provide a comparison with that whichTi-fioTa-lflv had been exposed to elevated temperature, and the re-THSO'Ia-IOV 0. e Q3 suits are shown in Table 3 below.

Table 3 THERMAL STABILITY OF VARIOUS TITANIUM-TANTALUM ALLOYS TensileProperties Bend Heat No. Composition Thermal Treatment Properties,

UTS, YS Eiong., Min. '1 K s.i. K s.i. Percent 1,400 F., Hr. AC 88 so 241,400 F., 14 Hr. AC+800 F., 24 Hrs. AC 145 145 0 1,400 F., 2 Hr. AC1,400 F., H1-. AC+500 F., 8 Hrs. AC 1,400 F., Hr. AC+600 F., 6 Hrs. AC1,400 F., Hr. AC+800 F., 24 Hrs. AC 1,400 F., /5 Hr. AC 44 23 1,400 F.,V Hr. A0+400 F., 0 Hrs. .40.- 100 04 is 1,400 F., Hr. -500 F., 6 Hrs.A01- 116 11s 10 1,400 F., V2 Hr. AC+800 F., 6 Hrs. 110.. 102 102 0 1,400F., V; Hr. AO+800 F., 24 Hrs. AC--. 143 1,400 F., /z Hr. AC 100 as 311,400 F., Hr. AC+500 F., 6 Hrs. AC.... 125 8 1,400 F., Hr. AO+600 F., 6Hrs. .40-.-- 139 1,400 F., Hr. AC 107 51 13 1,400 F., Hr. AC+600 F., 0Hrs. AC .1 119 7 1,4o0r., /4H1.Ac. a 1,400 F., HI. AC+600 F., 96 Hrs. AC

Table fi -Continued THERMAL STABILITY OF VARIOUS TITANIUM-TANTALUMALLOYS Tensile Properties I Bend Heat No. Oomposmon v I ThermalTreatment Properties,

UTS, YS, Elng., M111. T

K 5.1. K s.i. Percent Ti-40Ta-l0Cb-2V 1,400 F., 1 Hr. AG 103 50 18Ti-40Ta-10Cb-2V 4 1,400 F., 1 Hr. AC+600 F., 6 Hrs. AC. 116 115 11.T1-40Ta,100b-5V 1,400 F., 1 Hr. AG 89 84 16 T1-40Ta-10Cb-5V 1,400 F., 1Hr. AC+6OO F., 6 Hrs AC. 97 91 8 T1-40Ta-l0Ob-7V 1,400 F., Hr. AG 92 8613 T1-40Ta-100b-7V 1,400 F., Hr. AC+800 F., 24 Hrs. AC. 93 87 13Ti-40Ta-10Cb-12V 1,400 F., H1. AC 102 96 T140Ta-10Cb-12V 1,400 F., V;Hr. AC+800 F., 24 Hrs. AC. 103 100 I 15 T1-40Ta-10Cb-2OV 1,400 F., Hr.AC 119 111 11 T1-4OTa-1OOb-2OV 1,400 F., V, Hr. A0+s00 F., 24 Hrs. AC-125 118 17 T1-40Ta-100b-3C1 1,400 F., 1 H1. AC 110 101 12T1-40Ta-100b-3Cr 1,400 F., 1 Hr. AC+600 F., 6 Ers. AC. 111 109 9T1-40Ta-10Cb-30r 1,400 F., 1 Hr. Ac+s00 F., 6 Hrs. AC- 115 112 6T1-40Ta-10Cb-50r... 1,400 F., Hr. AC 93 91 16 TiTa-l0Cb-5Cr.. 1,400 F.,Hr. AC+600 F, Hrs. AC 98 95 16 Ti-40Ta-10Cb-50r- 1,400 F., Hr. AC-l-600F., 6 Hrs. AC 100 98. 15 Ti-EOTa-IOV 1,500 F2, H1. AC 106 102 15Ti-Ta-10V 1,500 F., Hr. AC+800 F., 48 Hrs. A0. 111 106 7 T1-55Ta-5Cr1,400 F., Hr. AC 121 117 8 Ti-Ta-5Cr 1,400 F., Hr. AC-l-GOO F., 6 Hrs.AC 124 120 8 Ti-40Ta-20Cb. 1,400 F., Hr, A Ti-40Ta-20Cb 1,400 F., Hr.AC+600 F., 24 Hrs. AC Ti-40Ta-20V 1,400 F., Hr. A

1,400 F., /2 Hr. AC-l-600 F., 24 Hrs. 140..-; 1,400 F., Hr. A 1,400 F.,H1'.AO+500 F., 24 Hrs. AC 1,400 F., Br. .40.. 1,400 F., Hr. AC+500 F.,24 Hrs. AC Ti-40Ta-10Cb-12V-2.1A1 1,400 F., V; Hr. AC; 1Ti-40Ta-100b-12V-2.1Al 1,400 F., V Hr. AC+500 F., 24 Hrs. ACTi-35Ta-200b-10V-L8Al 1,400 F., Hr. A0 119 118 Ti-35Ta-20Cb-10V-L8Al1,400 F., Hr. AC+800 F., 6 Hrs. AC 132 -128 Ti-35Ta-15Cb-10V-L8Al 1,400F., V2 Hr. AC 115 110 Ti-35Ta-150b-10V-L8Al 1,400 F., V Hr. Ac+s00 F., 6Hrs. AC 1- 119. 115 Ti-Ta-8.5V,-1.5Al 1,500 F., V Hr. AC Ti-60Ta-85V-1.5Al 1,500 F., V; Hr. AC+800 F., 0 Hrs AC Ti-Ia-8.5V-1.5Al 1,500 F.,Hr. AC+800 F., 6 Hrs. AC..- Ti-60Ta GV-1A1 1,500 F., Hr. ACTi-60Ta-6V-1Al 1,500 F., Hr. AO+800 F., 6 Hrs. AC Ti-50Ta-100b-6V-1Al1,500 F., V2 Hr. A 4. Ti-50Ta-1OGb-6V-1Al 1,500 F., Hr. AC+800 F., 6Hrs. AO Ti-40Ta-100b-1Fe 1,400 1 2% 11;.40 100 ,87 17 Ti-40Ta-100b-1Fe1,400 F., V; Er. AC+600 F., 6 Hrs. AC 134 134 1 Ti-40Ta-l0Cb-2IFe 1,400F., Hr. AC 113 110 17 Ti-40Ta-l0Cb'2Fe 1,400 F., H1. AC-l-GOO F., 6 Hrs.AO 119 117 1G Ti-40Ta-100b-2Fe 1,400 F., Hr. AC+800 F., 6 Hrs. AC 122'118 9 Ti-40Ta-1OCb-4Mn 1,400 F., Hr. A0 116 111 16 Ti-40Ta-10Cb-4Mn1,400 F., %,Hr. AC+600 F., 6 Hrs. A0 116 113 19 Ti-401a10Cb-4Mn 1,400F., 4 Hr. AC+O F., 24 Hrs. AC 123 114 11, Ti-40Ta-10Cb-6W 1,400 F., Hr.AC Ti-40Ta-10Cb-6W 1,400 F., $4 Hr. AC+600 F., 6 Hrs. AC

Ti-40Ta-100b-6W 1,400 F., Hr..AC+8OO F., 24 Hrs, AC

Brittle, no yield. 2 Brittle. w r 1 The results obtamecl on the 50%tltamurn, 5 0% tanelement anhances the corrosion res1stance somewhat astalum alloy, as wellas the 50% titanium, 40% tantalum, Will be seen byreference to Table 2.

10% colu-rnbium alloys showed a markedloss in ductility Further testswere run to determine the thermal statilities of alloys containingf betastabilizers, within the when these alloys were heated as low as 400 F.for 6 bility of alloys'of this invention under stress. This is a hours.and complete ,loss of ductility and glass hard brit- 50 characteristicthat is valuable when material is employed tleness after being heated to800 F.,for 24 hours. Heat to fabricate structural members which may berequired T-284, which was made from an alloy containing 70% to operateunder stress as well as at elevated temperatantalum, dropped'inelongation from 13% t0 7% after ture, as for instance autoclave parts.Specimens were heating for 6 hours at 600 F. In comparison, theducannealed and then maintained under stress of from 25,000 to 70,000psi; at temperatures of 500 F. and ranges hereindescribed, show little.significant reduction 600 F. for 150 hours. Comparison of ductilities,shown in ductility after heating up to 800 F. for 24 hours. byelongation percentages, indicated little difierence be- Those containing5 to 10% beta stabilizers show exceltween specimens of alloys of thisinvention only annealed lent retention of ductility, considering, ofcourse, the and after thermal stress treatment, While an alloy of limitsof possible testing error. Inclusion of up to about 40% Ta, 10% Cb,balance Ti (Heat 9187) showed com- 2% aluminum tends to improve thermalstability, and plete loss of ductility. The results of these tests areinclusionof up to this amount of this optional alloying shown in Table 4below.

. Table 4 THERMAL STRESS STABILITY OF'VARIOUS TITANIUM-TANTALUM ALLOYSSubsequent Tensile I I 3 Exposure Properties Heat 1 CompositionAnnealing Treatment Def.,

No. r Percent Stress, Time, UTS, YS, Eiong., K s.i. Hrs. K 5.1. K s.1.Percent Ti-40Ta-10cb- 25 150 Neg. 136 Ti-40Ta-10cb Tensile 44 28Tl-40Ta-10eb-2V. 25 150 Neg. 131 9 Ti-40Ta-10cb-2V. Tensile 103 50 13 25150 Neg 107 21 Ti-40Ta-l00b-5V Table 4Continued Annealing Treatment 1 1.1 1 1 1 1. 1n1 1 1 1 1 1 1 1 1 1 Ll inl l l l l inl l 1 1 1 1 1 1 1 1 11 1 1 1 1 n n n n u n n 11 n AAM u N n fir n m .M 1.11 1 RD N. v wmw newhaul M m 6 bob bloom. mmb Mb w CCCVV CCOCO Vvv 0 CO 0 OOOOOCCOOOOO..0.5.5.VV0 00 a ammawmwwmawwww aawaaw awn w wwwwwwawwwww Manama WM MHMMMMMMHMMMM HM T TTTTTTTTTTTT TTflTTT TT a a. mafi MMT TTTTTT columbiummaster alloy canbe used in its Its corrosion resistance is notappreciably ive the

Adequate corrosion It is extremely than 70% are employed, the corrosionresistant properties may correspond closely to those of pure tantalumbut at 75 the same time, due to increased alloying and processing Bend,Min. '1

der conium aplarge measure responsible for the corrosion Elong.,

Percent hen a comhereby. The

Ys, K 5.1.

lum and no columit may advantageously be employed un U'rs, K st.

tantalum is employed, a large Table Continued or, if part of thetantalum is replaced the tantalum content should be at least If morethan 70% If percentages of tantalum higher Mechanical Properties X6;2Iii6ifrIIII The alloy containing columbium replacing part of thetantalum has the advantage of reduced cost w bined tantalumproduction.

than the alloy containing tanta and The amounts of the various alloyingconstituents in thef positions of this invention are critical to obtaexpensive material.-

poorer bium,

ditions in which is may be exposed to less corros media than those usedfor test results.

com

benefits and desirable properties imparted t tantalum content incombination with the titan pears to be resistant properties of thealloys.

resistance will not be obtained if the tantalum content is less than 40%by columbium,

part of the extremely desirable low cost advantage of t alloys of thisinvention will be lost.

significant that the alloys of this invention provide corrosionresistant properties approaching those of pure tantalum, yet contain 70%or less of tantalum, which is very tantalum, num, balin this case 10%gagi g tantalum content has been replaced with colum- 3% Oxalic AcidBend, Min.l

3% Oxalic Acid combination inum, bal- 30% H3PO4 Elong., Percent rosionresistance and mechanialloys, before and after thermal in Table 5 below.

20% HCl UIS, YS, Ksi.

20% HCl- 1 Brittle; broke outside gage length.

sistance and thermal stability contains 8.5% vanadium, 1.5% alumRepresentative cor Table 5 ALLOY-50% Ta, 8.5% V, 1.5% A1, BALANCE TiMechanical Properties ALLOY-40% Ta, l0% Ob, 8.5% V, 1.5% A1, BALANCE TiA preferred alloy showing an excellent Year (48 hour test)..

year (48 hour test)..

of corrosion re 50% tantalum, 8.5% vanadium, 1.5% alum ance titanium. Asimilar alloy contains 50% 10% columbium,

ance titanium and it will be noted that of the bium. v

cal properties of these exposure, are tabulated Boiling..

Corrosion Resistance, Mils per As Annealed---" After 800 F. for 24 hoursBoiling Corrosion Resistance, Mile per costs, the more complexcompositions may show little, if any, significant cost advantage.

The percentages of beta stabilizing elements are critical to obtain thedisirable stability characteristics without affecting to an appreciabledegree the excellent corrosion resistant properties of the alloys. Lessthan 2% beta stabilizer will not provide suflicient increase in thermalstability to be appreciable or of practical importance, and more than20% beta stabilizer will adversely affect the corrosion resistance andin addition, some of the mechanical properties. A small amount ofaluminum within the limit stated will improve the corrosion resistance,although the reason for this effect is not precisely known. In addition,the small amount of aluminum contributes to providing thermal stabilityin the alloy since it will to some extent reduce the tendency forprecipitation of the omega phase which has a marked hardening efi'ect onthe beta matrix. More than 2.5% of aluminum will tend to more stronglystablize the alpha phase and reduce the beneficial effects of inclusionof beta stabilizers as hereinbefore described.

The alloy of this invention may be produced by any convenient method inwhich the constituents are rendered molten to provide an ingot ofhomogenous alloy composition. Arc melting procedures may be employed,and the titanium, tantalum and other alloying constituents may bepressed into compacts and these compacts assembled into an electrodewhich can be melted into a cold mold crucible by the well-knownconsumable electrode arc melting process. It should be pointed out,however, that a homogenous ingot is necessary to obtain uniformproperties, and the proper and desired effect produced by the variousalloy constituents. It will be appreciated that titanium and tantalumhave substantially different melting points and more than normaldifficulty may be encountered in producing an ingot which is free fromunmelted inclusions of the, higher melting point tantalum metal. Use oftantalum in relatively finely divided powdered form, so as to obtain aninitial relatively good dispersion of this material, will be helpful inproducing homogeneous materials; and in addition, remelting of the ingotperferably several times will be found also effective to produceacceptable homogeneity.

The alloys of this invention possess outstanding corrosion resistantproperties as will be evident from the data presented herein. At thesame time the thermal stability, as indicated by retention of ductilityafter exposure to temperatures up to 800 F., will be satisfactory forapplications involving exposure of products fabricated from these alloysat such elevated temperatures for a reasonable period of time, and alsoindicates a substantial immunity from thermal instability attemperatures of the order of those normally encountered in boilingaqueous solutions for an extremely long life period. It will beappreciated by those skilled in the art that an alloy of this inventioncan be used for long periods of time without fear of embrittlement undercorrosive conditions at elevated temperatures, as for example, whenemployed as structural or lining materials in autoclaves, and similarrelatively high temperature and pressure equipment, as well as beinguseful at temperatures encountered in contact with aqueous solutionseven up to their boiling point more or less indefinitely.

The alloys of this invention are characterized, in addition, bysubstantially higher tensile strength than shown by pure tantalum or bythe previously known alloys of V tantalum and titanium.

Inclusion of a beta stabilizing element markedly increases the yieldstrength and tensile strength of the alloy. This makes it possible forthinner and lighter structural or lining members to be employed Whileretaining similar strength and corrosion resistant properties. It willalso be found that the alloys of this invention are considerably lighterthan the pure tantalum which they are capable of replacing in manyapplications; and this is responsible for production of a greater volumeof fabricated material per pound; thus further reducing the cost of thealloy in useful form. It will be evident that a. pound of an alloyaccording to this invention will provide substantially more sheet of agiven thickness than can be obtained from a pound of pure tantalum. The

' other, less costly, elements.

We claim:

1. An alloy formed by melting its constituents characterized 'byresistance to corrosion by HCl indicated by a corrosion rate of lessthan 10 mils per year in boiling 20% HCl, 48 hour test, and by thermalstability indicated by substantial retention of ductility after exposureto temperatures up to about 800 F. consisting essentially of:

(a) about 40% by weight tantalum,

(b) about 10% by weight columbium,

(0) about 1.5% by weight aluminum, and

(d) about 8.5% by weight vanadium,

(e) balance titanium.

2. An alloy formed by melting its constituents characterized byresistance to corrosion by HCl indicated by a corrosion rate of lessthan 10 mils per year in boiling 20% HCl, 48 hour test, and by thermalstability indicated by substantial retention of ductility after exposureto temperatures up to about 800 F. consisting essentially of:

(a) about 50% by weight tantalum, (b) about 1.5% by weight aluminum, and

Reactive Metals V, 2 reprinted from Metallurgical Society Conferences,Proceedings of the Third Annual Conference sponsored by Niagara FrontierSection in cooperation with The Metallurgical Society, Aimme, Buffalo,New York, May 27-29, 1958, Interscience Publishers (pages 497-499 reliedupon).

1. AN ALLOY FORMED BY MELTING ITS CONSTITUENTS CHARACTERIZED BYRESISTANCE TO CORROSION BY HCL INDICATED BY A CORROSION RATE OF LESSTHAN 10 MILS PER YEAR IN BOILING 20% HCL, 48 HOUR TEST, AND BY THERMALSTABILITY INDICATED BY SUBSTANTIAL RETENTION OF DUCTILITY AFTER EXPOSURETO TEMPERATURES UP TO ABOUT 800*F. CONSISTING ESSENTIALLY OF: (A) ABOUT40% BY WEIGHT TANTALUM, (B) ABOUT 10% BY WEIGHT COLUMBIUM, (C) ABOUT1.5% BY WEIGHT ALUMINUM, AND (D) ABOUT 8.5% BY WEIGHT VANADIUM, (E)BALANCE TITANIUM.